1. Field of the Invention
This invention relates generally to discrete time radio frequency (RF) filtering, and more particularly to a method of improving antialiasing and adjacent channel interference filtering suitable for GSM (global system for mobile communications) applications, among others.
2. Description of the Prior Art
Discrete-time radio frequency (RF) is still a newly emerging field in wireless digital communications wherein analog RF signals that are transmitted over-the-air are directly sampled into a discrete-time sample stream suitable for digital signal processing. A typical wireless digital communications device would use analog filters, duplexers, mixers, analog-to-digital converters (ADC), and the like to convert the analog RF signals into a digital data stream that is suitable for digital signal processing. Resistors and capacitors, for example, are commonly employed to implement cascaded RC filters in a deep sub-micron process associated with the wireless digital communications device. Such use of resistors and capacitors however, is disadvantageous in that resistor and capacitor values do not track each other accurately in a deep sub-micron process, making it extremely difficult if not impossible to accurately control the pole/filter characteristics.
In view of the above, it would be both desirable and advantageous to provide a technique for mixing and/or combining components in a deep sub-micron process that provides the same functionality as the cascaded RC filter, but which provides better tracking capability than the cascaded RC filter.